Summary: Paxson and Schady examine the relationship between early cognitive development, socioeconomic status, child health, and parenting quality in a developing country. They use a sample of over 3,000 predominantly poor pre-school age children from Ecuador and analyze determinants of their scores on the Spanish version of the Peabody Picture Vocabulary Test (TVIP), a widely used test of language ability. The authors show that median age-normed test scores on the TVIP are much lower for older than younger children, and there is greater dispersion in scores among older children. They find that household socioeconomic characteristics, in particular wealth and parental education, are "protective"-children from wealthier households with more educated parents have higher scores. The associations of test scores with wealth and maternal education are larger for older children, suggesting that these factors have cumulative effects on cognitive ability. Last, the authors show that child health and measures of parenting quality are associated with performance on the TVIP. Children with lower hemoglobin levels perform worse on tests. Measures of parenting quality, in particular the degree to which parents are "responsive" and "harsh" toward children, and whether children are read to, account for a portion, although not the majority, of the association between socioeconomic status and cognitive development.